Count by hours until you can't count anymore without passing your end time
so, starting at 11:30 add an hour
Hour 1
11:30 + 1 hr = 12:30 am
Hour 2
Add another hour
12:30 + 1 hr = 1:30 pm.
Now, you can't add another hour or else you will pass up 2:12 pm. So, add up the hours that you got to get to 1:30. From, 11:30 to 1:30 is 2 hours.
Next, count by the half hour, or 30 minutes. So, from 1:30, add 30 minutes until you can't count anymore without passing 2:12
1:30 + 30 minutes = 2:00
Now, you can't add another 30, or else you will pass 2:12 pm. So, adding on the 30 minutes, from 11:30 am to 2:00 pm is 2 hours and 30 minutes.
Finally, you can add on the 12 minutes to get from 2:00 to 2:12
So, 30 minutes plus 12 minutes is 42 minutes
so, from 11:30 am to 2:12 pm is 2 hours and 42 minutes